Valuable documents such as security papers or e.g. banknotes, cheques, shares, papers having a security imprint, certificates, identity cards, passports, entrance tickets, travel tickets, vouchers, identification or access cards or the like can be provided with security features on their front side, their rear side and/or in a manner embedded in the material, in order to hamper or to prevent forgery thereof and to be able to check the authenticity thereof. In the exemplary case of a banknote, some of said security features, e.g. a region of the banknote that is printed with luminescent ink, may be machine-testable.
Conventional apparatuses for handling such banknotes which are installed e.g. in automated teller machines for issuing banknotes are equipped inter alia with systems that check the authenticity of the banknotes on the basis of the machine-readable security features in order to remove them from circulation, if appropriate, if a banknote is identified as counterfeit. In this case, the security features are detected by sensors, and the signals are processed and evaluated by a processing device of the system. In order to ensure reliable detection of the security features, the system has to be calibrated e.g. with regard to the security features to be checked. Since both the sensors, e.g. cameras, and components of the processing device, e.g. analogue-to-digital converters for the cameras, have tolerances, a joint calibration of the sensors with the processing device leads to a dependence of the calibration on characteristics of the sensors and of the processing device, that is to say that they are coordinated with one another by the calibration. For the case where one sensor is intended to be exchanged for another after calibration, e.g. on account of a failure of the sensor, in conventional systems the entire system has to be exchanged since a renewed calibration cannot be carried out with systems that have already been installed in an automated teller machine.
Consequently, in conventional systems there is a problem to the effect that in the event of a failure of a component of the system, the entire system has to be exchanged.